Limiting the exposure of oxygen-sensitive materials to oxygen can help improve the shelf life of many products, such as foods, beverages, and pharmaceuticals to suggest but a few. Polypropylene (PP) and polyethylene (PE) are common commodity polymers used for films and other plastic packaging. These polymers tend to have good moisture barrier properties, but are quite permeable to oxygen. In order to impart oxygen barrier characteristics to packaging using such commodity polymers, a barrier material or layer is often included as part of the packaging. For instance, ethylene vinyl alcohol (EVOH), nylon, metal films and other oxygen barrier layers may be combined with the PP or PE as a separate layer to form a multi-layer film or package. In a packaging film structure, however, using such additional barrier layers to block passage of oxygen tends to result in a relatively thick multilayer film. In many instances, for example, to impart oxygen barrier characteristics to a polypropylene or polyethylene film, an EVOH or nylon layer is adhered to polypropylene or polyethylene in a five layer laminate using adhesive tie layers to secure the EVOH or nylon to the polypropylene or polyethylene. One exemplary prior film laminate includes the following layers (in order): PP/tie/EVOH/tie/PP layers; or PE/tie/EVOH/tie/PE layers. Such thick laminates can be costly, limit packaging applications, and can limit the ability to recycle the films due to the EVOH or nylon components. Such prior oxygen barrier materials are considered passive products because they are configured to block the passage of oxygen through a film or other packaging material.
Other attempts to limit oxygen exposure to oxygen-sensitive materials uses oxygen scavenger materials. Oxygen scavenger materials form an active barrier because the oxygen scavenger does not necessarily block passage of oxygen, but is configured to react with and bind oxygen as it permeates the film or package. It is common to use a polyamide-metal catalyst oxygen scavenging system in polyesters to achieve an oxygen barrier. A common polyamide (monomers of amide groups in the polymer) is poly(m-xylene adipamide), which is commercially known as MXD6. However, while the polyamide-based oxygen scavengers work well in polyester (such as PET), they tend not to be compatible or miscible in many other polymers used for packaging. For example, MXD6 tends not to be compatible or miscible in polyolefins like polypropylene and polyethylene. Other known oxygen scavenging materials also tend not to be compatible or miscible with polyolefin materials. Incompatible materials may form multiple phase or non-uniform blends. It is believed that non-uniform dispersions of the oxygen scavenging materials in a polymer tend to limit the oxygen scavenging capability of existing chemistries when combined with polyolefin materials.
The oxygen scavenging films often include a catalyst, and in some instances, a co-catalyst in combination with an oxidizable substrate. In addition to the incapability of prior oxygen scavenging materials with polyolefin polymers, the catalyst and co-catalysts used with oxygen scavenger chemistries may not be sufficiently robust to be incorporated into a mono-layer polyolefin film using conventional film extrusion or molding processing. Often the oxygen scavenging composition cannot withstand the harsh processing and thermal conditions of a film extrusion process or molding process. Many components suitable for an oxygen scavenging system, even if compatible with the desired film forming polymers, may decompose or degrade at the temperatures typically used to form these polymers into films or molded structures. The decomposed or degraded materials tend not to function efficiently as a catalyst or co-catalyst.